The present invention relates to a variable valve actuating mechanism. More particularly, the present invention relates to a variable valve actuating mechanism having automatic lash adjustment.
Modern internal combustion engines may incorporate advanced throttle control systems, such as, for example, intake valve throttle control systems, to improve fuel economy and performance. Generally, intake valve throttle control systems control the flow of gas and air into and out of the engine cylinders by varying the timing, duration and/or lift (i.e., the valve lift profile) of the cylinder valves in response to engine operating parameters, such as engine load, speed, and driver input. Intake valve throttle control systems vary the valve lift profile through the use of variously-configured mechanical and/or electromechanical devices, collectively referred to herein as variable valve actuation (VVA) mechanisms. Several examples of particular embodiments of VVA mechanisms are detailed in commonly assigned U.S. Pat. No. 5,937,809 and U.S. Pat. No. 6,019,076, the disclosures of which are incorporated herein by reference.
Generally, a conventional VVA mechanism includes a rocker arm that carries an input cam follower, such as a roller. The input cam follower engages an opening or input cam lobe of a rotating input shaft, such as the engine camshaft, and transfers rotation of the input cam lobe to oscillation of the rocker arm toward and away from the input shaft in a generally radial direction. The oscillation of the rocker arm is transferred via a link arm to pivotal oscillation of an output cam relative to the input shaft. The pivotal oscillation of the output cam is transferred to actuation of an associated valve by an output cam follower, such as, for example, a roller finger follower. The rocker arm also carries a closing cam follower, such as, for example, a slider pad, that engages a closing cam lobe of the rotary input shaft. The closing cam follower transfers rotation of the closing cam lobe to the rocker arm, thereby ensuring that the output cam is pivoted back or returned to its starting or base angular orientation.
A desired valve lift profile is obtained by pivoting a control shaft into a predetermined angular orientation relative to a centerline thereof. A frame member is pivotally disposed on the input shaft, and is coupled at one end thereof to the control shaft and at the other end thereof to the rocker arm. The pivotal movement of the control shaft is transferred, via the frame member, rocker arm and link arm, to pivotal movement of the output cam relative to a central axis of the input shaft. Thus, pivoting the control shaft places the output cam into the base or starting angular orientation. The base or starting angular orientation of the output cam, in turn, determines the portion of the lift profile thereof that will engage the output cam follower during pivotal oscillation of the output cam. The lift profile of the output cam that engages the cam follower determines the valve lift profile.
Conventional VVA mechanisms may also include a lash adjustment means. The lash adjustment means is adjusted during assembly of the VVA mechanism and/or engine to reduce mechanism lash, i.e., clearances between the cam followers and their corresponding cam lobes that are larger than intended, and thereby compensate for manufacturing tolerances and/or component dimensional variation. The adjustment of the lash adjustment means during assembly of the mechanism or engine is time consuming and labor intensive. Periodic adjustment of the lash adjustment means is typically required thereafter, such as, for example, to compensate for wear and tear of mechanism components. Such further adjustment requires a vehicle owner to return the vehicle to a service provider for periodic maintenance.
Therefore, what is needed in the art is a VVA mechanism having a lash adjustment means that reduces and/or eliminates the need for manual adjustment of lash during assembly and/or installation of the VVA mechanism.
Furthermore, what is needed in the art is a VVA mechanism having a lash adjustment means that substantially reduces the need for periodic adjustment/maintenance to reduce/remove the lash from the VVA mechanism.
Still further, what is needed in the art is VVA mechanism having a lash adjustment means that automatically reduces/removes lash from the VVA mechanism.
Moreover, what is needed in the art is a VVA mechanism having an automatic lash adjustment means that substantially reduces and/or eliminates the need for periodic maintenance and/or manual adjustment in order to reduce/remove lash.
The present invention provides a variable valve actuation mechanism having an automatic lash adjusting means.
The present invention comprises, in one form thereof, an output cam pivotally disposed upon an input shaft. A first link arm is pivotally coupled at a first end thereof to the output cam. A rocker arm is pivotally coupled at a first end thereof to a second end of the link arm. A frame member is pivotally disposed upon the input shaft. Lash adjusting means include an eccentric pin and a force applying means. The eccentric pin pivotally couples together a first end of the frame member and a second end of the rocker arm. The force applying means applies a force upon the eccentric pin causing the eccentric pin to pivot which, in turn, adjusts the position of the rocker arm relative to the input shaft and thereby removes lash from the mechanism.
An advantage of the present invention is that the need for manual adjustment of lash during assembly of a VVA mechanism is substantially reduced.
Another advantage of the present invention is that the need for periodic adjustment/maintenance to reduce/remove lash in the VVA mechanism is substantially reduced.
A further advantage of the present invention is that lash is automatically reduced/removed from the VVA mechanism.
A still further advantage of the present invention is that the need for periodic maintenance and/or manual adjustment of the VVA mechanism in order to reduce/remove lash therefrom is substantially reduced.